Process for production of draw-ironed can

ABSTRACT

In a process for the production of a draw-ironed can, supposing that at the draw-ironing step, the blank thickness is A, the maximum thickness of the side wall of a cup-shaped body obtained by draw working of the first stage is B and the maximum thickness of the side wall of a cup-shaped body obtained by redraw working of the second stage is C, the increase of thickness B is controlled to up to 20% of thickness A and the increase of thickness C is controlled to up to 30% of thickness A, and supposing that the final thickness of the side wall of the draw-ironed can finally obtained by ironing working is D, the thickness reduction ratio of the side wall of the obtained draw-ironed can satisfies the following requirements: 
     
         (B-D)/B×100≦70%, 
    
     and 
     
         (C-D)/C×100≦70%. 
    
     According to this process, the surface roughness of the final can body is improved, barrel breaking is prevented at the ironing step, and a draw-ironed can having improved necking workability and flanging workability is obtained.

DESCRIPTION Technical Field

The present invention relates to a process for the production of adraw-ironed can. More particularly, the present invention relates to aprocess for the production of a draw-ironed can, in which the final canbody is improved in the surface roughness and the necking workabilityand flanging workability are improved.

Background Art

Draw-ironed cans (sometimes referred to as "DI cans" hereinafter) formedof a tin-deposited steel sheet (tinplate) or an aluminum sheet are usedin large quantities for beer cans and carbonated drink cans. These DIcans are prepared by draw-forming a metal blank into a cup having arelatively large diameter, redrawing the cup into a cup having a smalldiameter and subjecting the side wall portion of the cup to ironingworking 2 or 3 times. According to need, the prepared DI cans aresubjected to single-stage or multiple-stage necking working of reducingthe diameter of the opening and then to flanging working to obtain canbodies to which easy-open lids are wrap-seamed.

In the production of DI cans, draw-forming and redrawing areindispensable steps. At this draw-redraw forming, the metal sheet showssuch a plastic flow that the dimension increases in the height directionof the cup but the dimension decreases in the circumferential directionof the cup. Accordingly, in a cup obtained by draw-redraw forming, thereis observed a tendency that the thickness of the side wall portiongradually increases toward the top from the bottom and the thickness isextremely large at the top end (open end) of the side wall portion.

Accordingly, the following defects are brought about when theabove-mentioned redraw-formed cup is subjected to ironing working.

At the ironing step, the thickness of the side wall portion of the canis determined by the clearance between the radius of the outer surfaceof the punch and the radius of the inner surface of the die, and thethickness of the side wall portion is constant from the lower portion tothe upper portion. However, the thickness of the upper portion of thecup is larger than the thickness in the lower portion. Accordingly, theironing condition is severe and the thickness reduction ratio is high.At a high ironing ratio, barrel breaking is often caused at the ironingstep, and wrinkling and flange cracking are often caused in the upperportion where necking working and flanging working are performed,resulting in occurrence of insufficient sealing (leakage). Moreover, thesurface of the side wall of the can becomes rough and the metallic glossis degraded, and in order to prevent the exposure of the metal, acoating having a larger thickness becomes necessary.

Application of an organic paint to the metal blank in advance orlamination of an organic resin film on the metal blank in advance,instead of formation of a coating on the formed DI can, is desirable inview of the productivity and environmental sanitation. However, theconventional draw-ironing process is defective in that the adhesion ofthe organic coating is drastically reduced in the upper portion of theside wall and the metal exposure measured as the enamel rater value(ERV) becomes extraordinarily large.

DISCLOSURE OF THE INVENTION

It is therefore a primary object of the present invention to provide adraw-ironed can where the above-mentioned defects of the conventionaltechnique are overcome.

Another object of the present invention is to provide a draw-ironed canwhere the surface roughness of the final can body is improved, barrelbreaking is prevented at the ironing step and the necking workabilityand flanging workability are improved.

Still another object of the present invention is to provide a processfor the preparation of a draw-ironed can, in which the thicknessreduction ratio at the ironing step is controlled to a relativelyuniform level throughout the side wall of the cup from the lower portionto the upper portion.

A further object of the present invention is to provide a processespecially suitable for the draw-ironing working of a precoated metalblank.

In accordance with the present invention, there is provided a processfor the production of a draw-ironed can, characterized in that supposingthat at the draw-ironing step, the blank thickness is A, the maximumthickness of the side wall of a cup-shaped body obtained by draw workingof the first stage is B and the maximum thickness of the side wall of acup-shaped body obtained by redraw working of the second stage is C,increase of thickness B is controlled to up to 20% of thickness A andthe increase of thickness C is controlled to up to 30% of thickness A,and that supposing that the final thickness of the side wall of thedraw-ironed can finally obtained by ironing working is D, the thicknessreduction ratio of the side wall of the obtained draw-ironed cansatisfies the following requirements:

    (B-D)/B×100≦70%,

and

    (C-D)/C×100≦70%.

When the present invention is applied to a precoarted metal blank,particularly a thin metal sheet laminated with a polyester resin film,especially prominent effects can be attained.

As the means for controlling the increase of the thickness B and theincrease of thickness C within the above-mentioned ranges, in thepresent invention, there is preferably adopted a method in whichredrawing working is carried out in at least one stage by holding apreliminarily drawn cup between an annular holding member inserted intothe cup and a redrawing die, and relatively moving a redrawing punch,which is arranged coaxially with the holding member and redrawing die sothat the redrawing punch can enter in the holding member and come outtherefrom, and the redrawing die so that they are engaged with eachother, to draw-form the preliminarily drawn cup into a deep-draw-formedcup having a diameter smaller than that of the preliminarily drawn cup,wherein the curvature radius (R_(D)) of the working corner of theredrawing die is 1 to 2.9 times the thickness (t_(B)) of the metalblank, the curvature radius (R_(H)) of the holding corner of the holdingmember is 4.1 to 12 times the thickness (t_(B)) of the metal blank, flatengaging portions of the holding member and redrawing die with thepreliminarily drawn cup have a dynamic friction coefficient of from0.001 to 0.2, and the redraw ratio defined by the ratio of the diameterof the preliminarily drawn cup to the diameter of the redrawn cup is inthe range of from 1.1 to 1.5. However, the redrawing means that can beadopted in the present invention is not limited to the above-mentionedmethod.

Referring to FIG. 1 showing shapes and dimensions of formed bodies atrespective steps of the process for the production of a draw-ironed canaccording to the present invention, a blank 100 has a thickness A. Apreliminarily cup 101 obtained by draw working of the first stage has adiameter larger than that of a final draw-ironed can, and a bottom wall102 has the same thickness as the thickness A of the blank 100 but thethickness of a top portion 103 of the side wall is increased to themaximum thickness B by compression plastic flow. A redrawn cup 104obtained by redrawing working of the second stage has a diametersubstantially equal to that of the final draw-ironed can and a bottomwall has the same thickness as the thickness A of the blank, but thethickness of a top portion of the side wall is increased to the maximumthickness C by compression plastic flow by the redrawing of the secondstage. A can 107 has the thickness A at a bottom 108, but a side wall109 has a uniform thickness D controlled by the ironing working.

According to the present invention, the above-mentioned objects areattained by controlling the increase of the thickness B to up to 20%,preferably up to 15%, of the thickness A, controlling the increase ofthe thickness C to up to 30%, preferably up to 25%, of the thickness A,and controlling the final thickness of the side wall at the ironingworking so that the following requirements are satisfied:

    (B-D)/B×100≦70%                               (1)

and

    (C-D)/C×100≦70%                               (2)

As the result of our research, it has been found that in theconventional draw-ironing working process, the increases of thethickness B is about 24 to about 25% of the thickness A, and in thiscase, it is difficult to control the increase of the thickness C to upto 30% of the thickness A. In the conventional process, the increase ofthe thickness C is about 33 to about 34% of the thickness A, and in thiscase, the thickness reduction ratio in the portion of the thickness C bythe ironing process is excessively high and such defects as barrelbreaking at the ironing, wrinkling and cracking at the necking workingand flanging working and increase of the surface roughness are broughtabout. In the present invention, control of the increase of thethickness within the above-mentioned range is absolutely necessary forcontrolling the increase of the thickness C to up to 30% of thethickness A, but this is not sufficient for preventing occurrence of theabove-mentioned defects of the conventional process. In the presentinvention, all of the defects of the conventional process can becompletely overcome by controlling the increase of the thickness C up to30% of the thickness A.

In the present invention, it also in important that at the ironingworking, the final thickness D of the side wall of the can should be setso that the requirements of formulae (1) and (2) are satisfied. If thethickness reduction ratios expressed by the left-hand sides of formulae(1) and (2) exceed 70%, barrel breaking, generation of wrinkles orcracks at the necking or flanging working and increase of the surfaceroughness are caused.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) through 1(D) are diagrams illustrating drawing and ironingsteps.

FIGS. 2 and 3 are sectional views illustrating the main part at thedrawing working.

FIG. 4 is a sectional view illustrating the corner portion at thedrawing step.

FIG. 5 is a plot diagram where the curvature radius Rd of the cornerportion shown in FIG. 4 is plotted on the abscissa and the thicknesschange ratio at is plotted on the ordinate while the thickness t ischanged.

FIG. 6 is a sectional view showing a coated metal sheet used in thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2 illustrating the preliminarily drawing method usedin the present invention, a coated or uncoated metal sheet 1 is held bya preliminarily drawing die 2 and a blank holder 3, and the metal sheet1 is formed into a preliminarily drawn cup by a punch 4 movingrelatively to the preliminarily drawing die 2 so that the punch 4 isengaged with the preliminarily drawing die 2. In the present invention,in order to control the increase of the thickness B to up to 20% of thethickness A, the curvature radius R of the corner of the preliminarilydrawn cup is adjusted to 3.0 to 15.0 times the blank thickness A,especially 3.5 to 12.0 times the blank thickness by bending elongationof the side wall is effectively attained and the difference of thethickness between the lower and upper portions of the side wall isdiminished.

Referring to FIG. 3 illustrating the redrawing method used in thepresent invention, the preliminarily drawn cup 5 formed by theabove-mentioned preliminarily drawing method is held by an annularholding member 6 inserted into this cup and a redrawing die 7 locatedbelow the holding member 6. A redrawing punch 8 is arranged coaxiallywith the holding member 6 and redrawing die 7 so that the redrawingpunch 8 can enter into the holding member 6 and come out therefrom. Theredrawing punch 8 and redrawing die 7 are relatively moved so that theyare engaged with each other.

By this redrawing, the side wall of the preliminarily drawn cup 5 ispassed through a curvature corner 10 of the annular holding member 6from a peripheral surface 9 thereof, bent vertically inwardly of theradius, passed through a portion defined by an annular bottom face 11 ofthe annular holding member 6 and a top face 12 of the redrawing die 7and bent substantially vertically in the axial direction by a workingcorner 13 of the redrawing die 7 to form a deep-draw-formed cup 14having a diameter smaller than that of the preliminarily drawn cup 5,and simultaneously, the side wall is bend-elongated to reduce thethickness of the side wall.

In this case, if the curvature radius (R_(D)) of the working corner ofthe redrawing die is adjusted to 1 to 2.9 times the thickness A of themetal blank, especially 1.5 to 2.9 times the thickness A of the metalblank, reduction of the thickness by bending elongation of the side wallis effectively accomplished and simultaneously, the difference of thethickness between the lower and upper portions is diminished and uniformthickness reduction is attained in the entire side wall, whilecontrolling the increase of the thickness C to up to 30% of thethickness A.

Referring to FIG. 4 illustrating the principle of bending elongation, ametal sheet 15 is forcibly bent along a working corner of a redrawingdie having a curvature radius R_(D) under a sufficient back tension. Inthis case, no strain is produced on a surface 16 of the metal sheet 15on the side of the working corner, but a surface 17 on the side oppositeto the working corner undergoes a strain by pulling. The quantity ε_(s)of this strain is given by the following formula: ##EQU1## wherein R_(D)represents the curvature radius of the working corner and t representsthe sheet thickness.

The surface (inner surface) 17 of the metal sheet is elongated by ε_(s)by the working corner but the other surface (outer surface) is elongatedin the same quantity as ε_(s) just below the working corner by the backtension. Since the metal sheet is thus bend-elongated, the thickness ofthe metal sheet is reduced, and the thickness change ratio ε_(t) isgiven by the following formula: ##EQU2##

From this formula (4), it is seen that reduction of the curvature radiusR_(D) of the working corner is effective for reducing the thickness ofthe metal sheet, that is, the smaller R_(D), the larger is |ε_(t) |.Furthermore, it is seen that if the curvature radius R_(D) of theworking corner is constant, the larger is the thickness t of the metalsheet passed through the working corner, the larger is the thicknesschange |ε_(t) |.

FIG. 5 is a graph in which the curvature radius R_(D) of the workingcorner is plotted on the abscissa and the thickness change ratio ε_(t)is plotted on the ordinate while changing the thickness t of the metalsheet. This curve obviously indicates the above-mentioned fact.

Supposing that the thickness of the metal sheet supplied to the workingcorner is t_(o) and the thickness of the sheet having the thicknessreduced by bending elongation is t₁, this thickness t₁ is given by thefollowing formula: ##EQU3## incidentally, in the upper portion of theside wall of the preliminarily drawn cup, the thickness is increasedover the standard thickness (blank thickness) t_(B) by the influence ofthe compression in the radial direction and this thickness is given bythe following formula:

    T.sub.o =(1+α)t.sub.B                                (6)

wherein α represents the thickness index.

Therefore, the reduced thickness t₁ is given by the following formula:##EQU4##

The ratio of t₁ in case of α=0 to t₁ in case of α≠0 is given by thefollowing formula: ##EQU5## From formula (8), it is understood thatreduction of R_(D) exerts the function of controlling the variationratio of the thickness in the bend-elongated side wall to a small value.More specifically, in the case where t_(B) is 0.18 mm and α is 0.1, ifR_(D) is 2 mm, Ratio is 1.091 but if R_(D) is 0.5 mm, Ratio is 1.072.Thus, it is understood that reduction of R_(D) is prominently effectivefor controlling the variation of the thickness and uniformalizing thethickness.

In other words, since the ratio of the thickness of the preliminarilydrawn cup to the standard thickness (t_(S)) is 1+α, the thicknessvariation-controlling ratio is given by the following formula: ##EQU6##When the value of formula (9) is calculated with respect to theabove-mentioned instance, it is seen that the value is 0.009 in case ofR_(D) =2 mm and is 0.028 in case of R_(D) =0.5 mm, and that the effectattained in the latter case is about 3.2 times as high as the effectattained in the former case.

As is apparent from the foregoing illustration, the present invention isbased on the finding that reduction of the curvature radius (R_(D)) ofthe working corner of the redrawing die is effective for uniformalizingthe thickness of the side wall after the bending elongation. In the casewhere the value of R_(D) is too large and exceeds the above-mentionedrange, the degree of the thickness reduction of the side wall and theuniformity of the thickness of the side wall are insufficient. On theother hand, if the value of R_(D) is too small and below theabove-mentioned range, breaking of the blank is readily caused in theworking corner of the die at the redrawing step and the objects of thepresent invention are hardly attained.

In the present invention, it is preferred that draw-forming be thencarried out so that the curvature radius (R_(H)) of the holding corner10 of the holding member 6 is 4.1 to 12 times, especially 4.1 to 11times, the thickness (t_(B)) of the metal blank, flat engaging portionsof the holding member 6 and redrawing die 7 with the preliminarily drawncup have a dynamic friction coefficient (u) of 0.001 to 0.20, especially0.001 to 0.10, and the draw ratio defined by the ratio of the diameterof the shallow-draw-formed cup to the diameter of the deep-draw-formedcup is 1.1 to 1.5, especially 1.15 to 1.45.

In order to perform sufficient bending elongation by the working cornerof the redrawing die, it is indispensable that a back tension should beapplied so that the metal sheet is supplied while the metal sheet isbent precisely along this working corner. This back tension is given bythe sum of (1) the forming load on the flat sheet at the side wall ofthe preliminarily drawn cup, (2) the substantial blank holding load and(3) the resisting load against deformation of the preliminarily drawncup to the deep-draw-formed cup. Of course, the sum of these forcesshould not be so large as causing breaking of the metal sheet but shouldbe such that blending elongation can be effectively accomplished.Furthermore, a certain balance should be maintained among these threeforces.

The curvature radius R_(H) of the holding corner 10 participates in theabove-mentioned forming load (1) and the formability. Namely, if thecurvature radius R_(H) is below the above-mentioned range, breaking ofthe sheet and damage of the surface are often caused. If the curvatureradius R_(H) exceeds the above-mentioned range, wrinkles are readilyformed. Thus, if R_(H) is outside the above-mentioned range, redrawforming is not satisfactorily performed. However, if this curvatureradius R_(H) is controlled within the above-mentioned range, redrawforming can be performed smoothly while giving a sufficient backtension.

The dynamic friction coefficients (μ) of the annular surface 11 of theholding member 6 and the annular face 12 of the redrawing die 7participate in the above-mentioned substantial blank holding force (2).The substantial blank holding force is a force effectively acting forcontrolling wrinkles generated with the contraction of the size of themetal sheet in the circumferential direction thereof, which isrepresented by the product of the force applied between the holdingmember and redrawing die and the dynamic friction coefficient (μ) of theabove-mentioned surfaces. If the dynamic friction coefficient (μ)exceeds the above-mentioned range, necking breaking of the metal sheetis readily caused, and if the dynamic friction coefficient (μ) is belowthe above-mentioned range, formation of wrinkles cannot be controlled.However, if the dynamic friction coefficient (μ) is adjusted within theabove-mentioned range, it is possible to give a back tension necessaryfor bending elongation while controlling formation of wrinkles orbreaking of the metal sheet.

The redraw ratio defined by the ratio of the diameter (b) of theshallow-draw-formed cup to the diameter (a) of the deep-draw-formed cupparticipates in the above-mentioned deformation-resisting load (3). Ifthis redraw ratio (b/a) is below the above-mentioned range, it isdifficult to obtain a deep-draw-formed can and it also is difficult toimpart a large back tension necessary for bending elongation. If theredraw ratio (b/a) exceeds the above-mentioned range, the deformationresistance is too large and breaking of the bending elongation is oftencaused. By adjusting the redraw ratio (b/a) within the above-mentionedrange, deep-draw forming can be performed at a high efficiency, breakingof the metal sheet can be prevented, and a back tension necessary forhigh bending elongation can be given.

As is apparent from the foregoing description, by adjusting thecurvature radius (R_(D)) of the corner portion of the redrawing die to asmall value, adjusting the curvature radius (R_(H)) of the cornerportion of the holding member to a large value, adjusting the dynamicfriction coefficient (μ) of the holding member and die and the redrawratio (b/a) within specific ranges and adjusting these conditionsintegrally, deep-draw forming, reduction of the thickness of the sidewall and uniformalization of the thickness can be attained. In thiscase, if redraw forming is carried out in a plurality of stages, forexample, up to 4 stages, the thickness of the side wall is moreuniformalized.

According to the present invention, a deep-draw-formed can having anentire draw ratio of 0.2 to 4.0, especially 2.0 to 3.5, can be obtained.The draw ratio referred to herein is a value given by the followingformula: ##EQU7## Furthermore, the thickness of the side wall of theredrawn cup can be reduced to 60 to 95%, especially 65 to 90%, of theblank thickness (t_(B)) on the average, and the increase of thethickness C can be controlled to up to 30%, especially up to 25%, of thethickness A.

At draw forming or redraw forming, preferably, a coated or uncoatedmetal sheet or a cup is coated with an aqueous lubricant formed bydispersing a surface active agent or oil.

Draw forming can be carried out at room temperature, but it is generallypreferred that draw forming be carried out at a temperature of 20° to95° C., especially 20° to 90° C.

Then, ironing working is carried out in a single stage or a plurality ofstages by using an ironing punch and an ironing die in combination sothat the thickness D of the side wall satisfies the requirements offormulae (1) and (2). It is preferred that the entire ironing ratio,that is, the total ironing ratio R_(I) defined by the following formula:##EQU8## be at least 40%, especially at least 50%. At ironing working,it is preferred that cooling and lubrication be effected by supplying anaqueous lubricant formed by dispersing a surface active agent or oil inwater to the redrawn cup and the ironing die.

The formed can is subjected to various workings such as doming, neckingand flanging to obtain a can barrel for a two-piece can.

In the present invention, various surface-treated steel sheets andsheets of light metals such as aluminum can be used as the metal sheet.

As the surface-treated steel sheet, there can be used steel sheetsobtained by annealing a cold-rolled steel sheet, subjecting the annealedsheet to secondary cold rolling and subjecting the cold-rolled steelsheet to at least one surface treatment selected from zinc deposition,tin deposition, nickel deposition, electrolytic chromate treatment andchromate treatment. As a preferred example of the surface-treated steelplate, there can be mentioned an electrolytically chromate-treated steelsheet, and an electrolytically chromate-treated steel sheet comprising10 to 200 mg/m² of a metallic chromium layer and 1 to 50 mg/m²(calculated as metallic chromium) of a chromium oxide layer isespecially preferably used because this steel sheet is excellent in thecombination of the coating adhesion and corrosion resistance. Anotherexample of the surface-treated steel sheet is a hard tinplate having adeposited tin amount of 0.5 to 11.2 g/m², and preferably, this tinplateis subjected to a chromate treatment or a chromate/phosphate treatmentso that the deposited chromium amount is 1 to 30 mg/m² as metallicchromium.

Not only a so-called pure aluminum sheet but also an aluminum alloysheet can be used as the light metal sheet. An aluminum alloy sheethaving excellent corrosion resistance and workability comprises 0.2 to1.5% by weight of Mn, 0.8 to 5% by weight of Mg, 0.25 to 0.3% by weightZn and 0.15 to 0.25% by weight of Cu, the balance being aluminum. Whenthese light metal sheets are precoated, it is preferred that they besubjected to a chromate treatment or a chromate/phosphate treatment sothat the chromium amount is 20 to 300 mg/m² as metallic chromium.

The blank thickness A of the metal sheet differs according to the kindof the metal and the use or size of the vessel. However, it is generallypreferred that the blank thickness be 0.10 to 0.50 mm, and it isespecially preferred that the blank thickness A be 0.10 to 0.30 mm incase of a surface-treated steel sheet or 0.15 to 0.40 mm in case of alight metal sheet.

The above-mentioned metal sheet can be directly used, but if aprotecting coating of a resin is formed on the metal sheet prior to drawforming, deep draw forming and ironing working can be performed withoutsubstantial damage of the protecting coating layer. The protectingcoating can be formed by applying a protecting paint or laminating athermoplastic resin film.

An optional protecting paint comprising a thermosetting resin orthermoplastic resin can be used as the protecting paint. For example,there can be mentioned modified epoxy paints such as a phenol-epoxyresin and an amino-epoxy paint, vinyl and modified vinyl paints such asa vinyl chloride/vinyl acetate copolymer, a partially saponified vinylchloride/vinyl acetate copolymer, a vinyl chloride/vinyl acetate/maleicanhydride copolymer, an epoxy-modified vinyl paint, anepoxy/amino-modified vinyl paint and an epoxy/phenol-modified vinylpaint, acrylic resin paints, and synthetic rubber paints such asstyrene/butadiene copolymer. These paints can be used singly or in theform of a mixture of two or more of them.

These paints are applied to a metal blank in the form of an organicsolvent solution such as an enamel or a lacquer or an aqueous dispersionor aqueous solution by roller coating, spray coating, dip coating,electrostatic coating or electrophoretic deposition. Of course, if theresin paint is a thermosetting paint, the paint can be baked accordingto need. In view of the corrosion resistance and workability, it ispreferred that the thickness of the protecting coating be 2 to 30 μm,especially 3 to 20 μm (dry state). Moreover, in order to improve thedrawing-redrawing workability, a lubricant can be incorporated into thecoating.

As the thermoplastic resin film to be laminated, there can be mentionedfilms of olefin resins such as polyethylene, polypropylene, anethylene/propylene copolymer, an ethylene/vinyl acetate copolymer, anethylene/acrylic ester copolymer and an ionomer, films of polyesterssuch as polyethylene terephthalate, polybutylene terephthalate and anethylene terephthalate/isophthalate copolymer, films of polyamides suchas nylon 6, nylon 6,6, nylon 11 and nylon 12, a polyvinyl chloride film,and polyvinylidene chloride film. These films may be undrawn films orbiaxially drawn films. It is generally preferred that the thickness ofthe thermoplastic film be 3 to 50 μm, especially 5 to 40 μm. Laminationof the film on the metal sheet can be accomplished by fusion bonding,dry lamination or extrusion coating, and if the adhesiveness (heatfusion bondability) between the film and metal sheet is poor, forexample, a urethane adhesive, an epoxy adhesive, an acid-modified olefinadhesive, a copolyamide adhesive or a copolyester adhesive can beinterposed between them.

An inorganic filler (pigment) can be incorporated into the coating orfilm to be used in the present invention for hiding the metal sheet andassisting the transmission of the blank-holding force to the metal sheetat the drawing-redrawing forming.

As the inorganic filler, there can be mentioned inorganic white pigmentssuch as rutile titanium oxide, anatase titanium oxide, zinc flower andgloss white, white extender pigments such as baryte, precipitated barytesulfate, calcium carbonate, gypsum, precipitated silica, aerosil, talc,calcined clay, uncalcined clay, barium carbonate, alumina white,synthetic mica, natural mica, synthetic calcium silicate and magnesiumcarbonate, black pigments such as carbon black and magnetite, redpigments such as red iron oxide, yellow pigments such as sienna, andblue pigments such as ultramarine and cobalt blue. The inorganic fillercan be incorporated in an amount of 10 to 500% by weight, especially 10to 300% by weight, based on the resin.

FIG. 6 shows an example of the coated metal sheet preferably used in thepresent invention. Formation films 19a and 19b such as chromate-treatedfilms are formed on both the surfaces of a metal substrate 18, and aninner face coating 20 is formed on the surface, to be formed into aninner surface of the can, through the formation film 19a, and on thesurface to be formed into an outer surface of the can, an outer facecoating comprising a white coating 21 and a transparent varnish 22 isformed through the formation film 19b.

The top layer 20 on the surface to be formed into an inner surface ofthe DI can is preferably formed of a polyester film. The polyester resincoating layer comprises ethylene terephthalate units in an amount of 75to 99% of total ester recurring units, remaining 1 to 25% of esterrecurring units being derived from at least one acid component selectedfrom the group consisting of phthalic acid, isophthalic acid,terephthalic acid, succinic acid, azalaic acid, adipic acid, sebacicacid, dodecadionix acid, diphenylcarboxylic acid2,6-naphthalene-dicarboxylic acid, 1,4-cyclohexane-dicarboxylic acid andtrimellitic anhydride, and at least one saturated polyhydric alcoholselected from the group consisting of ethylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, propylene glycol, polytetramethyleneglycol, trimethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane and pentaerythritol. This polyester resinis formed into a film by a known extruder and is used as an undrawnpolyester resin film, but in order to improve the barrier property ofthe polyester resin film, it is preferred that the formed film be drawnin both of the longitudinal direction and the lateral direction and bethen thermally set. The thickness of the polyester resin film is notparticularly critical, but preferably, the thickness of the polyesterresin film is 10 to 50 μm. If the thickness is smaller than 10 μm, thelamination adaptability is drastically degraded, and the workability isinsufficient and the film cannot follow up with DI working. If thethickness exceeds 50 μm, the polyester resin film is economicallyadvantageous over epoxy pains widely used in the filed of manufacture ofcans. It is preferred that the softening-initiating temperature of thepolyester resin film be in the range of from 170° to 235° C. By thesoftening-initiating temperature referred to herein is meant thetemperature at which the needle begins to penetrate into the polyesterresin film when the temperature is elevated at a rate of 10° C./min byusing a thermal mechanical analysis apparatus (TMA100 supplied by SeikoDenshi Kogyo). If the softening-initiating temperature is higher than235° C., the workability of the polyester resin film is degraded and agreat number of cracks are formed at the DI working. On the other hand,if the softening-initiating temperature is lower than 170° C., when theouter surface is printed after the DI working and the print layer isbaked, since the baking temperature is higher than thesoftening-initiating temperature of the polyester resin film, theoperation adaptability is drastically degraded and the polyester resinfilm cannot be practically used. Also the crystal-melting temperature ofthe polyester resin film is important, and it is preferred that thistemperature be in the range of from 190° to 250° C. By thecrystal-melting temperature referred to herein is meant the temperatureat which the maximum peak depth of the endothermic peak is observed whenthe temperature is elevated at a rate of 10° C./min by a differentialscanning calorimeter (SS10 supplied by Seiko Denshi Kogyo). If thecrystal-melting temperature of the polyester resin film is higher than250° C., the polyester resin film per se becomes very rigid and theworkability is drastically degraded. If the crystal melting temperatureis lower than 190° C., the heat resistance of the polyester resin filmper se is degraded, and when heating is effected by outer surfaceprinting or the like, the mechanical strength is drastically degraded,and necking and flanging to be conducted afterward are impeded.

Also the orienting property of the polyester resin film is a factorimportant for deciding the workability of the polyester resin film.Namely, it is especially preferred that the in-plane orientationcoefficient be in the range of from 0 to 0.100. The in-plane orientationcoefficient referred to herein is determined by a refractometer and isdefined by (refractive index in longitudinal direction refractive indexin lateral direction)÷2--refractive index in thickness direction.

If the in-plane orientation coefficient is larger than 0.100, theworkability of the polyester film is drastically degraded and a greatnumber of cracks are formed at the ironing working, and the polyesterresin film cannot be practically used. Also the mechanical properties ofthe polyester resin film are important, and it is especially preferredthat the elongation at break of the polyester resin film be 150 to 500%and the strength at break be 3 to 18 kg/mm₂. The elongation at break andstrength at break of the polyester resin can be determined by carryingout the tensile test at a constant temperature of 25° C. at a pullingspeed of 100 mm/min by an ordinary tensile tester.

If the elongation at break of the polyester resin film is lower than150%, the workability of the polyester resin film is drasticallydegrated and cracks are readily formed by a severe ironing working suchat the DI working. If the elongation at break is higher than 500%,thickness unevenness is readily caused at the formation of the film andbecause of this thickness unevenness, the film is easily damaged at anironing working such as the DI ironing. Similar phenomena are observedwith respect to the strength at break of the polyester resin film. Ifthe strength at break is higher than 18 kg/mm², the workability andadhesion of the polyester resin film are drastically degraded, andcracking and peeling are readily caused by ironing. If the strength atbreak is lower than 3 kg/mm², since the toughness is lost in thepolyester resin film and scratches are readily formed in the polyesterresin film at the can-manufacturing step, with the result that thepolyester resin film is damaged from such scratches if ironing isfinally carried out. It is preferred that the formation films 19a and19b as the adhesion undercoat below the polyester resin coating layer bechromium oxide hydrate layers. This chromium oxide hydrate layer can beformed by applying a known chromate treatment to a steel sheet, a steelsheet deposited with tin, nickel, chromium, zinc or aluminum, a steelsheet deposited with an alloy of such metals, a steel sheet depositedwith a plurality of layers of such metals, or a metal sheet formed bydepositing a metal as mentioned above on a steel sheet and heat-treatingthe metal-deposited steel sheet to form a metal diffusion layer on thesurface of the steel sheet. In view of the adhesion and corrosionresistance of the polyester resin coating layer after the DI processing,it is preferred that the chromium oxide hydrate layer be present in anamount of 0.005 to 0.050 g/m², especially 0.010 to 0.030 g/m², asmetallic chromium. If the amount of the chromium oxide hydrate layer issmaller than 0.005 g/m² or larger than 0.050 g/m² as metallic chromium,the laminated polyester resin film is often peeled at the DI working,especially the ironing working, and no good results can be obtained. Inthe present invention, the presence of the chromium oxide hydrate layeris indispensable for maintaining a good adhesion of the polyester resincoating layer. In the case where a high corrosion resistance isrequired, in view of the anticorrosive effect or from the economicalviewpoint, it is preferred that below the chromium oxide hydrate layer,there be present a plating layer of metallic chromium, tin, nickel, zincor aluminum, a plating layer of an alloy of such metals or a pluralityof plating layers of such metals, or a metal diffusion layer be formedas the surface layer of the steel sheet by heat-treating such a metalplating layer as mentioned above. Preferably, the deposited amount is0.01 to 0.30 g/m² as metallic chromium, 0.01 to 5.6 g/m² as metallictin, 0.03 to 1.0 g/m² as metallic nickel, 0.50 to 2.0 g/m² as metalliczinc or 0.01 to 0.70 g/m² as metallic aluminum. In the case where aplating layer, alloy layer or metal diffusion layer as mentioned aboveis formed, if the metal amount is below the above-mentioned lower limit,no substantial anticorrosive effect is attained, and if the metal amountexceeds the upper limit, an effect of highly improving the corrosionresistance is not conspicuous and the continuous productivity of asurface-treated steel sheet is reduced.

In the present invention, it is indispensable that a plating layer of aductile metal such as tin, nickel, zinc or aluminum should be formed onthe surface to be formed into the outer surface of the DI can, where theresin is brought into contact with the ironing die. The reason is thatthe ductile metal plating layer shows a lubricating effect at theironing working and renders it possible to perform the ironing workingat a high ironing ratio. In view of the general workability at theproduction of DI cans, it is especially preferred that a tin platinglayer be formed. If the tin amount is at least 0.5 g/m², the DI workingis not impeded. The upper limit of the tin amount is not particularlycritical, but from the economical viewpoint, it is preferred that thetin amount be up to 11.2 g/m². The tin plating player may be either aplating layer which has been subjected to a fusion treatment or aplating layer not subjected to a fusion treatment. In order to preventoxidation of this plating layer, the plating layer may be subjected to achemical treatment, so far as the ironing property is not degraded. Thetreatment is sufficient if the plating layer is immersed in a solutionof sodium dichromate, as conducted in case of a tinplate sheet for a DIcan.

Furthermore, in the present invention, it is indispensable that at thestep of laminating the polyester resin film on the above-mentionedsurface-treated steel sheet, the steel sheet should be heated at atemperature of from the crystal-melting point of the polyester resinfilm to a temperature higher by 50° C. than the crystal-meltingtemperature of the polyester resin film. If the temperature of the steelsheet is lower than the crystal-melting point of the polyester resinfilm, the polyester film is not tightly bonded to the chromium oxidehydrate film, and at the DI working, the polyester resin film is peeled.If the temperature of the steel sheet exceeds the temperature higher by50° C. than the crystal-melting temperature of the polyester resin film,the laminated polyester resin film is readily thermally deteriorated,and the barrier property for the content of the can is degraded and thecan body is readily corroded. If the polyester resin film used in thepresent invention is laminated on the steel sheet heated at atemperature of from the crystal-melting temperature of the polyesterresin film to the temperature higher by 50° C. than the crystal-meltingtemperature of the polyester resin film, the polyester resin film ispartially or completely rended unoriented or amorphous, and this ispreferable for the DI workability. The polyester resin film can becooled or gradually cooled after the lamination.

In the production of the DI can of the present invention, it is notabsolutely necessary that an adhesive should be coated on one surface ofthe polyester resin film. However, a DI can composed of a steel sheetlaminated with a polyester resin film coated with a compositioncomprising at least one polymer containing at least one group selectedfrom an epoxy group, a hydroxyl group, an amide group, an ester group, acarboxyl group, a urethane group, an acrylic group and an amino group inthe molecule in a dry amount of 0.1 to 5.0 g/m² is preferable becausethread-like rusting caused when the DI can is allowed to stand still ina high-temperature and high-humidity atmosphere for a long time can beprevented. If the coated amount is smaller than 0.1 g/m² in the drystate, the adhesive force is unstable, and if the coated amount islarger than 5.0 g/m² in the dry state, there is a risk of peeling of thepolyester resin coating layer at the forming working of the DI can.

As is apparent from the foregoing description, in the process for theproduction of a draw-ironed can according to the present invention, theincrease of the thickness B of the side wall of the draw cup iscontrolled to up to 20% of the thickness A, the increase of thethickness C of the side wall of the redrawn cup is controlled to up to30% of the thickness A and the thickness D of the side wall of the finaldraw-ironed can is controlled within a specific range at the ironingstep, whereby the thickness reduction ratio at the ironing step can becontrolled relatively uniformly throughout the side wall of the cup fromthe bottom to the top. Accordingly, the surface roughness of the finalcan body is improved and breaking of the barrel is prevented at theironing step, and a draw-ironed can having improved necking workabilityand flanging workability can be obtained. Moreover, even when an organicresin-coated sheet is used, the organic resin coating layer is notpeeled and cracking is hardly caused, and a draw-ironed can having anexcellent corrosion resistance can be obtained.

Examples Example 1

A tinplate sheet having a thickness of 0.30 mm, a tempering degree ofT-2.5 and inner and outer surface deposited with 5.6 g/m² of tin wasdraw-ironed under the following forming conditions.

(Forming Conditions)

1. Blank diameter: 123.5 mm

2. Working conditions of first stage drawing

Draw ratio: 1.82

Clearance between punch and drawing die: 0.32 mm

Radius of shoulder of drawing die: 1.0 mm

Blank-holding force: 1 ton

3. Working conditions of second stage redrawing

Draw ratio: 1.29

Clearance between punch and drawing die: 0.30 mm

Radius of shoulder of redrawing die: 1.0 mm

Blank-holding force: 1 ton

4. Ironing punch diameter at ironing: 52.64 mm

5. Total ironing ratio: 64.04%

Then, doming and trimming were carried out according to customaryprocedures, and degreasing and washing were carried out and the innerand outer surfaces were coated. Then, necking and flanging were carriedout to obtain a barrel for a two-piece can.

The obtained results are shown in Table 1. No trouble was caused and agood draw-ironed can was obtained.

Example 2

Drawing-ironing working was carried out in the same manner as describedin Example 1 except that the radia (R and R_(d)) of the shoulders of thedrawing and redrawing dies and the blank-holding forces were changed.The forming conditions adopted were as described below. The obtainedresults are shown in Table 1.

(Forming Conditions)

1. Blank diameter: 123.5 mm

2. Working conditions of first stage drawing

Draw ratio: 1.82

Clearance between punch and drawing die: 0.32 mm

Radius of shoulder of drawing die: 1.0 mm

Bland-holding force: 2 ton

3. Working conditions of second stage redrawing

Draw ratio: 1.29

Clearance between punch and redrawing die: 0.8 mm

Blank-holding force: 2 ton

4. Diameter of ironing punch at ironing: 52.64 mm

5. Total ironing ratio: 64.0%

Comparative Example 1

Draw-ironing was carried out in the same manner as described in Example1 except that the radia (R and R_(d)) of the drawing and redrawing dies,the punch/die clearance and the blank-holding forces were changed tothose adopted in the conventional method. The forming conditions were asdescribed below. The obtained results are shown in Table 1.

(Forming Conditions)

1. Blank diameter: 123.5 mm

2. Working conditions of first stage drawing

Draw ratio: 1.82

Clearance between punch and drawing die: 0.43 mm

Radius of shoulder of drawing die: 4.0 mm

Blank-holding force: 1 ton

3. Working conditions of second stage redrawing

Draw ratio: 1.29

Clearance between punch and redrawing die: 0.39 mm

Radius of shoulder of redrawing die: 2.0 mm

Blank-holding force: 0.8 ton

4. Diameter of ironing punch at ironing: 52.64 mm

Total ironing ratio: 64.0%

                  TABLE 1    ______________________________________                  Example                         Example  Comparative                  1      2        Example 1    ______________________________________    Forming of DI Can    increase of thickness B (%)                    10.6     9.7      25.3    increase of thickness C (%)                    16.0     15.3     33.3    (B-D)/B × 100 (%)                    67.5     67.2     71.3    (C-D)/C × 100 (%)                    69.0     69.3     73.0    barrel break ratio (%)                    0        0        0.9    roughness of inner surface                    0.10     0.15     0.25    of can (Ra, μm)    Necking Working    wrinkling ratio (%)                    0        0        1.5    Flangeing Working    flange craking ratio (%)                    0        0        0.5    Coating    coverage of paint                    good     good     bad    ______________________________________

Example 3

A laminated sheet was prepared in the following manner.

A film comprising a chromium oxide hydrate layer in an amount of 0.017g/m² as metallic chromium as the upper layer and a metallic chromiumlayer in an amount of 0.10 g/m² as the lower layer was formed on onesurface of cold-rolled band steel sheet having a thickness of 0.30 mm, atempering degree of T-2.5 and a width of 300 mm by a known electrolyticchromate treatment, and tin was deposited in an amount of 5.6 g/m² onthe other surface. The surface-treated band steel sheet was heated at220° C. by using a roll heater and a biaxially oriented polyester film(polycondensate of ethylene glycol with 80% of terephthalic acid and 20%of isophthalic acid) having a thickness of 25 μm was laminated on thesurface having the chromium oxide hydrate layer, and the laminated steelsheet was immediately cooled with water. The obtained polyesterresin-coated steel sheet was subjected to drawing and ironing under thesame forming conditions as described in Example 1 so that the innersurface of the DI can was the polyester resin coating surface.

The obtained results are shown in Table 2. It is seen that a DI canhaving excellent characteristics was obtained.

Example 4

Both the surface of the same cold-rolled band steel sheet as used inExample 3 were deposited with 5.6 g/m² of tin, and the tin-depositedsurface to be formed into the inner surface of the DI can was subjectedto a known electrolytic chromate treatment to form a chromium oxidehydrate layer in an amount of 0.007 g/m² as metallic chromium as theupper layer on the tin layer, followed by water washing and drying. (Thetin-deposited surface to be formed into the outer surface of the DI canwas subjected to the dipping chromate treatment). The surface-treatedband steel sheet was heated at 220° C. by a roll heater. The samepolyester resin film as used in Example 3 was coated with a polymercomposition under conditions described below, and the coated film waslaminated on the surface subjected to the electrolytic chromatetreatment. Draw-ironing working was carried out under the same formingconditions as described in Example 2 so that the polyester resincoatedsurface was formed into the inner surface of the DI can. (Conditions forCoating Polymer Composition on Polyester Resin Film)

Polymer composition: 80 parts of an epoxy resin having an epoxyequivalent of 3000 and 20 parts of a p-cresol type resol. the solidcontent being 9%

2. Dry weight of polymer composition: 0.2 g/m²

3. Drying temperature after coating of polymer composition: 100° C.

Example 5

One surface of the same cold-rolled band steel sheet was deposited with3.0 g/m² of nickel according to known procedures, and the other surfacewas subjected to a known electrolytic chromate treatment to form a filmcomprising a chromium oxide hydrate layer in an amount of 0.010 g/m² asmetallic chromium as the upper layer and a metallic chromium layer in anamount of 0.055 g/m² as the lower layer, followed by water washing anddrying (the nickel-deposited surface was subjected to the dippingchromate treatment). The surface-treated band steel sheet was heated at250° C., and a biaxially oriented polyester film (polycondensate ofethylene glycol with 85% of terephthalic acid and 15% of isophthalicacid) was laminated on the surface subjected to the electrolyticchromate treatment. Draw-ironing was carried out under the same formingconditions as described in Example 1 except that the following changeswere made, so that the polyester resin-coated surface was formed intothe inner surface of the DI can.

1. Working conditions of first stage drawing

Clearance between punch and drawing die: 0.30 mm

Radius of shoulder of drawing die: 0.8 mm

Blank-holding force: 2 tones

2. Working conditions of second stage redrawing

Clearance between punch and drawing die: 0.32 mm

Radius of shoulder of redrawing die: 0.8 mm

Blank-holding force: 0.8 tone

Example 6

One surface of the same cold-rolled band steel sheet as used in Example3 was deposited with 0.5 g/m² of tin according to known procedures andwas then deposited with 0.16 g/m² of nickel according to knownprocedures, and simultaneously, the other surface was deposited with 3.0g/m² of nickel. Furthermore, the two-layer-deposited surface wassubjected to a known electrolytic chromate treatment to form a filmcomprising a chromium oxide hydrate layer in an amount of 0.025 g/m² asmetallic chromium as the upper layer and a metallic chromium layer in anamount of 0.030 g/m² as the layer, followed by water washing and drying(the thick nickel-deposited surface was subjected to the dippingchromate treatment). A polyester resin film (polycondensate of ethyleneglycol with 90% of terephthalic acid and 10% of isophthalic acid) havinga thickness of 30 μm was coated with a polymer composition underconditions described below, and the coated film was laminated on thesurface subjected to the electrolytic treatment. The obtained polyesterresin-coated steel sheet was subjected to draw-ironing working under thesame forming conditions as described in Example 1 except that thefollowing changes were made, so that the polyester resin coated surfacewas formed into the inner surface of the DI can. (Conditions of Coatingof Polymer Composition)

1. Polymer composition: 70 parts of an epoxy resin having an epoxyequivalent of 2500 and 30 parts of a polyamide resin (Veranide 115), thesolid content being 11%

2. Dry weight of polymer composition: 2.0 g/m²

3. Temperature for drying polymer composition: 80° C.

(Forming Conditions)

1. Working conditions of first stage drawing

Clearance between punch and drawing die: 0.30 mm

Radius of shoulder of drawing die: 0.6 mm

2. Working conditions of second stage redrawing

Clearance between punch and redrawing die: 0.32 mm

Radius of shoulder of drawing die: 0.8 mm

Blank-holding force: 0.8 ton

Comparative Examples 2 through 5

THE POLYESTER RESIN=COATED STEEL SHEETS OBTAINED IN Examples 3 through 6were draw-ironed under the same forming conditions as described inComparative Example 1 so that the polyester resin coated surface wasformed into the inner surface of the DI can.

The DI cans having the polyester resin-coated surface as the innersurface, prepared in Examples 3 through 6 and inner surface, prepared inExamples 3 through 6 and Comparative Examples 2 through 5, wereevaluated according to the following test methods. The obtained resultsare shown in Table 2.

(1) Degree of Exposure of Metal to Inner Surface of DI Can

The obtained DI can was degreased, washed and dried and a 1% solution ofsodium chloride maintained ar 25° C. was filled in the DI can. A certainvoltage of 6.3 V was applied between the DI can as the positiveelectrode and a stainless rod as the negative electrode, and the degreeof exposure of the metal was evaluated based on the flowing electriccurrent (mA).

(2) Storage Test

The obtained DI can was degreased, washed and dried, and the DI can wasthen subjected to flanging working. Coca Cola was filled in the can to adepth of 90% of the can height. An epoxy-phenolic paint was coated in adry thickness of 10 μm and baked on an aluminum sheet, and the formedaluminum lid was wrap-seamed to the can. The can was stored at 37° C.for 3 months, and the quantity of dissolved iron was measured and thecorrosion state of the side wall of the can was observed.

As is apparent from the foregoing, also in case of a DI can having thepolyester resin-coated surface as the inner surface, according to thepresent invention, barrel breaking is not caused, the neckingworkability and flanging workability are improved, peeling of thepolyester resin coating layer is not caused and cracking is notsubstantially caused in the polyester resin coating layer is caused, anda draw-ironed can having an excellent corrosion resistance can beobtained.

                                      TABLE 2    __________________________________________________________________________                     Exam-                         Exam-                              Exam-                                  Exam-                     ple ple  ple ple  Comparative                                              Comparative                                                     Comparative                                                            Comparative                     3   4    5   6    Example 2                                              Example 3                                                     Example                                                            Example    __________________________________________________________________________                                                            5    Deposited amount (g/m.sup.2) on outer                     Sn 5.6                         Sn 5.6                              Ni 3.0                                  Ni 3.0                                       Sn 5.6 Sn 5.6 Sn 5.6 Sn 5.6    surface    Film amount (g/m.sup.2) on outer    surface    plating of lowermost layer                     not Sn 5.6                              not Sn 0.5                                       not    Sn 5.6 not    Sn 0.5                     formed   formed                                  Ni 0.16                                       formed        formed Ni 0.16    metallic Cr      0.100                         0    0.055                                  0.030                                       0.100  0      0.055  0.030    Cr oxide hydrate 0.017                         0.007                              0.010                                  0.025                                       0.017  0.018  0.010  0.025    Polyester Film    thickness (μm)                     25  **25 30  **30 25     **25   30     **30    softening-initiating temperature                     176 176  192 212  176    176    192    212    (°C.)    crystal-melting temperature (°C.)                     215 215  239 241  215    215    239    241    in-plane orientation coefficient                     0.024                         0.024                              0.065                                  0.086                                       0.024  0.024  0.065  0.086    elongation (%) at break                     330 330  210 172  330    330    210    172    strength (kg/mm.sup.2) at break                     8.2 8.2  12.3                                  14.5 8.2    8.2    12.3   14.5    Forming of DI Can    increase of B (%)                     10.6                         9.7  4.7 1.0  ← 25.3 →    increase of C (%)                     16.0                         15.3 10.3                                  7.0  ← 33.3 →    (B-D)/B × 100 (%)                     67.5                         67.2 65.6                                  64.3 ← 71.3 →    (C-D)/C × 100 (%)                     69.0                         69.3 69.8                                  67.6 ← 73.0 →    Characteristics    metal exposure (mA)                     0.03                         0.08 0.15                                  0.50 31.0   29.0   342    438    amount (ppm) of dissolved iron                     0.02                         0.05 0.23                                  0.65 2.5    5.2    13.0   8.5    corrosion state  good                         good good                                  good pitting                                              pitting                                                     pitting                                                            pitting    __________________________________________________________________________     Note **: polymer composition was coated on polyester resin film

What is claimed is:
 1. A process for the production of a draw-ironed canwhich comprises:(i) draw-forming a metal sheet blank having a thicknessA into a preliminarily drawn cup with a side wall having a maximumthickness B while controlling the increase in the thickness B up to 20%of the thickness A, (ii) redrawing the preliminarily drawn cup into adeep-draw-formed cup having a diameter smaller than that of thepreliminarily drawn cup, and with the side wall having a maximumthickness C while controlling the increase of the thickness C up to 30%of the thickness A, and (iii) ironing the deep-draw-formed cup into adraw-ironed can with the side wall having a thickness D so that thetotal ironing ration R_(I) defined by the following formula: ##EQU9## isat least 40% and that the following requirements:

    (B-D)/B×100≦70%, and

    (C-D)/C×100≦70%

are satisfied.
 2. A process according to claim 1, wherein the processcomprises ironing the deep-draw-formed cup in a single stage or aplurality of stages by using a ironing punch and an ironing die incombination, and cooling and lubricating the deep-draw-formed cup andthe ironing die, at the ironing stage, using an aqueous lubricantcomprising a dispersion of a surface active agent or an oil in water. 3.A process according to claim 1, wherein the side wall of the finallyobtained draw-ironed can has an average surface roughness of 0.05 to0.20 microns.
 4. A process according to claim 1, wherein the metal sheetcomprises a polyester resin film-laminated thin sheet.